The skin under the fingernail at the base of the nail is pulling away from the finger?

Onycholysis. Most common causes are trauma (tapping long fingernails on keyboard), frequent exposure to water, & harsh chemicals (nail polish remover). Certain diseases can cause it as well: psoriasis, overactive thyroid, fungal infxns. Drugs like tetracycline or fluoroquinolones (cipro, et al) can cause it. See following site for treatment suggestions: http://www.Drugs.Com/health-guide/onycholysis.Html.
Many possibilites. Some causes of nail separation may include trauma, infection, and reaction or side effect of certain medications. Have them evaluated by a professional and get the appropriate treatment.